The present invention relates to a closing plate of a battery provided with a safety valve for explosion-proof of a closed battery, wherein protection of the safety valve is achieved by applying a protection film to a metal substrate of the closing plate so that the explosion-proof mechanism of the safety valve may not suffer damage, and relates to a battery using it.
With an increasing demand for electronic devices that are made much smaller in size, are portable and have enhanced performance, closed batteries with high energy density have been more popularly used as power sources for such electronic devices. Since the closed battery uses an alkali metal such as lithium as a material for positive and negative electrodes thereof, its outer container has a sealed structure so that the alkali metal such as lithium may not react with water in the atmosphere.
Such a closed battery of a sealed structure the advantage of being storable, but conversely, it is not free from problems resulting from the very high sealability thereof. That is, if the closed battery is exposed to high temperature or mishandled, the internal pressure thereof is sometimes abnormally elevated, which causes the battery itself to burst.
For instance, when the battery if supplied with more than a rated current to be overcharged, or is mishandled to short circuit the positive electrode terminal and the negative electrode terminal thereof, inducing a large current in the battery, the electrolyte is sometimes decomposed to generate gas in the battery container of such sealed structure as mentioned above. If the battery container is filled with such gas, the internal pressure of the battery is abnormally elevated and the closed battery itself may finally burst.
There is so far known a closing plate of a battery provided with an explosion-proof prevention mechanism or a safety valve for releasing such generated gas so as to prevent the burst of the closed battery as mentioned above. For example, Japanese Patent Laid-open Publication No. HEI-5-84025 teaches a safety valve device for a closed battery in which a positive electrode terminal constituting a closing plate of a battery, is provided with a gas releasing hole, and to which a metal foil is welded for making the device explosion-proof. In this disclosure, the closing plate is provided with a safety valve functioning such that if the internal pressure of the battery is elevated, the above mentioned metal foil ruptures so as to release the internal pressure through the above mentioned gas releasing hole of the positive electrode terminal, thereby reducing the internal pressure.
However, in the above mentioned closing plate provided with the safety valve, the metal ion is made extremely thin, so there arises a problem of the metal foil easily rupturing by even a common impact.
For instance, when the closing plate is assembled into a battery in the manufacturing operation for completion of a closed battery, or when a user inserts a battery into an eletronic device, impact is erroneously applied to the safety valve, which sometimes damages the safety valve.
Therefore, it is an object of the present invention to provide a closing plate of a battery, wherein protection for a safety valve is achieved by a relatively simple means of attaching a protection film to a metal substrate of the closing plate so that the explosion-proof mechanism of the safety valve may not suffer damage in normal handling.
To achieve the above mentioned object, there is provided a closing plate of a battery, the surface of which is covered with a protection film.
Further, there is provided a closing plate of a battery in which the protection film has previously been provided with a cut.
There is also provided a closing plate of a battery comprising a metal surface, a metal foil which is laminated to the lower surface of said metal substrate, and a protection film attached to the upper surface of said metal substrate and which protective film has previously provided with a cut in a prescribed shape.
Further, there is provided a battery using any of the closing plates as described above.